Furuno Marine Radar - Manual (Page 14)

3. INTERPRETING THE DISPLAY
This section provides the information necessary for
interpreting the display.
Radar Picture and Target Properties
The strength of the reflected echo depends not only
on the height and size of the target, but also its shape,
material composition and angle at which the radio
pulse strikes. The size of the target actually has little
to do with the reflected echo. If the radio pulse strikes
it at a right angle, even a small target will return
a strong echo provided that the material is a good
reflector of RF energy.
A return echo will be weak if the angle at which the
radio wave strikes a target is small. For example,
flat surfaces such as sandy beaches, sandbars and
mudbanks have almost no area that can reflect
energy back to the Radar. Conical surfaces, such as
lighthouses, generate weak return echoes because their
shape diffuses most of the radiated energy. Because of
their poor reflecting properties, flat or conical surfaces
do not return an echo suitable for range determination.
Radar sees only the near side of targets. For example,
it cannot show you what is behind a sea wall or an
island. The echo of a mountain peak may appear on
the Radar display as a peninsula or small island. The
Radar image is not always as it seems - you should
always exercise caution when interpreting the display.
Target material and reflected echo
Generally, steel objects return a very strong echo
while reefs and water return weak echoes. The
weakest echoes come from wood and fiberglass
objects. In summary, non-metallic objects or those
that are flat or conical in shape do not make good
Radar targets, and the Radar may display only weak,
intermittent echoes - or it may not display them at all.
Precipitation
Rain, snow and hail may return echoes which appear
on the display as a blurred or cluttered area. You can
suppress them by adjusting the A/C RAIN control, or
lowering the sensitivity.
Influence of Waves and Precipitation
On short range, a mass of echoes covers the central
part of the display. This is caused by echoes from
waves, called sea clutter. The higher the waves the
more extensive the sea clutter on the display. In most
cases it is more pronounced to the windward side of
the vessel. To suppress sea clutter, use the A/C SEA
control. Always leave a little sea clutter on the display
to be sure weak target echoes are not erased.
ARPA and AIS
ARPA is an acronym that stands for Automatic Radar
Plotting Aid. The ARPA functions as a collision
avoidance tool, tracking individual Radar targets and
plotting their course and speed in order to determine
the closest point of approach (CPA) and time to
closest point of approach (TCPA) to own vessel. Data
such as course, speed, range, bearing, CPA and TCPA
can be called up in a data box on the screen simply by
selecting the target of interest.
AIS is an acronym that stands for Automatic
Identification System. The AIS system is used to
exchange vessel and navigation data including vessel
name and call sign, length and beam, position with
accuracy indication and integrity status, course, speed,
heading and ROT and other specific information, all
in real time. Data is shared with other nearby ships as
well as coastal VTS (Vessel Traffic Service) stations.
Unlike ARPA, which is dependent upon Radar returns
to track targets, AIS targets are acquired and tracked
via VHF (radio) signal. This means that AIS-equipped
targets that are partially or totally obscured from the
sweep of the Radar can still be acquired and tracked if
within VHF coverage.
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It’s a well known fact that if you
want to catch fish you need to know
how to find them, and in order to
find the fish, you need to locate
the birds - the undisputed masters
of fish finding technology. What
is less clear is exactly how to go
about targeting birds with Radar, a
tool normally reserved for collision
avoidance. This section will remove
some of the mystery surrounding the
subject.
The first thing to think of when
considering bird-tracking Radar is
antenna beamwidth. Remember
that the narrower the beamwidth,
the greater target discrimination
you will have. For this reason,
dome antennas are not as adept
at tracking birds as a comparable
open array antenna. As the length of
the antenna radiator increases,
beamwidth becomes narrower, so
a larger antenna will invariably offer
better target discrimination.
Experience and practice will make
you a bird-finding machine, but to
get there you need to start with the
basics. For the novice, it is best to
practice these techniques on a clear
day with calm seas. It is easiest to
first visually locate a flock of birds
that you want to target.
To target the birds, set the Radar to
a mid- or long-range. Next, increase
the Gain control until you see noise
on the display. This will appear as
a blanket of small specks. You will
need to leave the Gain turned all
the way up, thus setting the receiver
for maximum sensitivity in order to
detect birds. Resist the temptation
to turn up the AC/Sea or AC/Rain to
drop out the noise. Flocks of birds
may look like dense, recurring noise
rather than a solid target, but you
should be able to see them clearly.
This is what you will be looking for
when you don’t have a visual cue as
to where the birds are feeding.
If your Radar is capable of operating
in True Motion, do so. You will be
stabilizing the
display, and you
will be able to
tell if the flock
is travelling in
a straight line
looking for bait
pods or if they
have found their
target school and
are feeding.
When operating
in Head Up or
True Motion, be
sure to turn on
your target trail
function and set
it for long trails
to help track
travelling flocks.
Practice these techniques and soon
you will be scouting your fishing
spots just like the pros.
These birds were targeted using the Furuno 1954C
NavNet Radar. True Color is highly desirable when
targeting birds, as demonstrated above; these flocks were
easily picked out in red against the blanket of clutter.
Radar Factoids - UHD Digital Radar Radar Factoids - UHD Digital Radar
Furuno’s NavNet 3D integrates Ultra High Definition
(UHD) Digital Radar that facilitates fully automatic,
high-precision Gain, Sea/Rain Clutter and Tuning
control that allow the auto mode to adapt to a variety
of sea-states for hands-free operation and ultimate
performance.
One amazing features of Furuno UHD Digital Radar
is ‘Real Time’ dual range Radar display. NavNet 3D
simultaneous scanning technology allows dual
progressive scan to display and update two Radar
pictures, both long and short range, at the same
time as opposed to the alternating update methods
of typical conventional dual range Radars. This
can be used to have one screen with the gain set
to locate birds and buoys, while you use the other
Radar screen to navigate.
Targeting Birds With Your Furuno Radar
UHD™ offers crystal clear, noise-free target presentation with
automatic real-time digital signal processing. Antenna rotation
speed (24/36/48 rpm) is automatically shifted to the appropriate
pulse length.
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